1. Field of the Invention
The present invention relates to a wing structure comprising an assembly which is basically constituted of a main airfoil and a lift augmenting device in the form of a flap articulated at the trailing edge of the airfoil so as to facilitate a high degree of lift to be imparted to the wing responsive to deployment of the flap. More particularly, the invention is directed to a novel configuration of a trailing edge flap for a wing structure, particularly an aircraft wing, wherein the upper surface of the flap is imparted an out-of-contour or curvilinearly raised configuration during periods of being stowed in the main airfoil whereby upon deployment of the flap into its deflected operative position will enhance the ability of the flap to derive an improvement in lifting capability and efficiency in comparison with presently conventional high lift trailing edge flaps. The invention is also directed to a method of augmenting the high lift capabilities of trailing edge flaps which are operatively articulated to the main airfoils of aircraft wings so as to provide for an improved overall lifting characteristic for the aircraft wing structure.
As is well known in the aircraft and aerospace technology in both military and commercial aircraft wing design applications, high lift, high performance aircraft wing structures include main airfoils which are in most instances equipped with high lift devices, such as trailing edge flaps operatively articulated to the main airfoil, and wherein the trailing edge flaps are ordinarily positioned in a stowed condition in the trailing end or cove portion of the main airfoil of the wing during cruise operation of the aircraft. During landing or take-off of the aircraft, the flaps are deployed into their high lift augmenting positions in that the flaps are articulated so as to be deflected downwardly relative to the main airfoil of the aircraft wing to which the trailing edge flaps are connected; for instance, such as by being movable on tracks and/or rotatable about hinges.
Ordinarily, the high lift devices, such as the trailing edge flaps of the wing structure, are each configured so as to have at least the upper surface thereof constitute a smooth continuation of the aerodynamic surface of the main airfoil when stowed therein during high speed cruise operating modes of the aircraft. Consequently, the trailing edge flap chord-wise cross-sectional geometry provides for relatively flat taperingly converging upper and lower flap surfaces, with a highly curved leading end joining the divergent front ends of the flat surfaces, and all of the flap surface curvature being normally concentrated within the forward 30-40% of the length of the trailing edge flap chord.
For instance, for slotted flaps, an opening is created between the trailing end of the main airfoil and the leading end or forward curvilinear surface of the trailing edge flap when the flap is deployed so as to be deflected downwardly relative to the main airfoil into its high lift mode, such as during aircraft landing or take-off, thereby causing a flow of air to be accelerated upwardly trough the slot and to stream over the surface of the flap, mixing with and energizing a flow of air streaming over the main airfoil. In this instance, the slot produces a high velocity airflow which must be directed so as to ideally closely follow the contour along the upper surface of the trailing edge flap. However, the high degree of curvature which is present at the leading end of the trailing edge flap is subject to a tendency to produce a pressure gradient along the upper surface of the flap which retards the airflow, thereby causing the boundary layer which is present on the surface of the flap to either thicken or even to separate from the flap. In connection with the foregoing, a thick or heavy boundary layer reduces the amount of turning which the airflow experiences, and the added lift imparted to the aircraft wing which is due to the flap deployment resultingly decreases. The reduction in the lift is evidenced as a decrease in the additional lift due to the flap as the angle of attack is increased; for instance, for constant flap deflection, or as a so-called "roll-off" in the flap lift increment with an increasing flap deflection, such as at a constant angle of attack. This, in essence, considerably reduces the effectiveness and degree of efficiency of the high lift which is desired as a result of the flap deployment; in essence, the downward deflection of the flap relative to the main airfoil from its stowed normal cruise condition in the latter.
2. Discussion of the Prior Art
Although various high lift devices for aircraft wing structures are known in this technology; for example, in the provision of trailing edge flaps or leading edge flaps which are articulated to a main high performance or high lift airfoil, these currently developed lifting augmenting devices or wing flaps generally do not exhibit the degree of efficiency desired in the deployment of the high lift devices, in essence, the aerodynamically optimized configured flap surface structures which are articulated to the main airfoil.
U.S. Pat. No. 3,831,886 to Burdges et al. discloses a leading edge high lift device in the shape of a foreflap articulated to a main airfoil of an aircraft wing, and which foreflap is adapted to be pivoted relative to the airfoil so as to enable high lift operation without adversely affecting the high speed cruise performance of the aircraft.
U.S. Pat. No. 3,208,693 to Riedler et al. discloses a lift augmenting device in the form of a leading edge flap slot configuration which will increase the lift of the airfoil upon being extended therefrom.
U.S. Pat. No. 3,897,029 to Calderon discloses an airfoil with a double-slotted leading end flap which is adapted to be employed in operative cooperation with a multi-slotted trailing edge slot structure in order to provide improved high lift coefficients during landing and take-off of an aircraft, and which discloses various basic shapes and proportions in conjunction with intended physical applications.
U.S. Pat. No. 4,995,575 to Stephenson discloses a wing trailing edge flap mechanism which is adapted to provide a double-slotted configuration during deployment of the trailing edge flap upon being extended from its stowed condition in the main aircraft wing airfoil during normal cruise configurations.
U.S. Pat. No. 3,743,219 to Gorges discloses a high lift leading edge device in the form of a leading edge wing flap which is adapted to be extended into its deployed condition so as to assume a desired non-uniform degree of curvature and to thereby enhance the lifting characteristics for the aircraft wing.
Finally, U.S. Pat. No. 5,178,348 to Bliesner discloses a contoured wing and trailing edge flap assembly in which the flap is adapted to be deflected into its deployed condition, and which the flap incorporates a contoured upper surface to counteract any adverse effects of wake-producing devices positioned upstream of a slot which is formed between the trailing end of the airfoil and the leading end of the deployed trailing edge flap so as to produce a desired pressure distribution and thin boundary layer over the upper surface of the trailing end flap.
Although all of the foregoing aircraft wing structures incorporating either leading edge flaps or trailing edge flaps which are articulated to the main airfoil portion of the wing and are deployable in order to provide for augmentation of the lifting coefficients of the wing during landing or take-off modes, the various devices are subject to the drawbacks in that they are configured so as not to fully utilize the high lift characteristics of which such flap structures are deemed to be capable and thereby fail to adequately realize their full efficacies.